Django Rest Framework分页极其缓慢

Question

我在Django Rest框架中进行了分页,看起来速度非常慢.Count看起来像罪魁祸首,由于表中数百万行,每次返回都要花费数百毫秒.

我使用postgresql作为数据库.有没有办法不计算行数仍然使用分页？如果我手动过滤了查询集,则在启用此功能之前性能很好.

Answer 1

问题是，用于计数的查询与用于获取数据的潜在复杂查询相同。这样比较浪费。PageNumberPagination在Paginator内部使用 Django 自己的。

为了使计数查询更简单，覆盖分页器类 DRF 使用：

from django.core.paginator import Paginator
from django.utils.functional import cached_property
from rest_framework.pagination import PageNumberPagination

class FasterDjangoPaginator(Paginator):
    @cached_property
    def count(self):
        # only select 'id' for counting, much cheaper
        return self.object_list.values('id').count()


class FasterPageNumberPagination(PageNumberPagination):
    django_paginator_class = FasterDjangoPaginator

Answer 2

覆盖get_paginated_response分页类的方法,不包括计数.您可以参考基本实现了的PageNumberPagination类来看看你应该返回什么.

from rest_framework.pagination import PageNumberPagination
from collections import OrderedDict # requires Python 2.7 or later

class PageNumberPaginationWithoutCount(PageNumberPagination):
    # Set any other options you want here like page_size

    def get_paginated_response(self, data):
        return Response(OrderedDict([
            ('next', self.get_next_link()),
            ('previous', self.get_previous_link()),
            ('results', data)
        ]))

然后在你的settings.py,设置DEFAULT_PAGINATION_CLASS你的新分页课程.

DEFAULT_PAGINATION_CLASS = 'path.to.PageNumberPaginationWithoutCount'

此方法用于分页文档中的示例.

编辑:从下面的评论中听起来这可能不足以阻止慢速sql查询,所以你可能还需要覆盖paginate_queryset.

Answer 3

如果你不需要计数，下一个和上一个链接就可以了，可以使用以下自定义类。

import sys
from collections import OrderedDict

from django.core.paginator import Paginator
from django.utils.functional import cached_property
from rest_framework.pagination import PageNumberPagination
from rest_framework.response import Response


class CustomPaginatorClass(Paginator):
    @cached_property
    def count(self):
        return sys.maxsize


# To Avoid large table count query, We can use this paginator class
class LargeTablePagination(PageNumberPagination):
    django_paginator_class = CustomPaginatorClass

    def get_paginated_response(self, data):
        return Response(OrderedDict([
            ('page', self.page.number),
            ('results', data)
        ]))